feat: desacoplar launcher del registro estatico de agentes

Introduce un registro global de reglas en agents/registry.go con
Register() y GetRules(). Cada paquete de agente se auto-registra
via init(), eliminando la necesidad de editar manualmente el map
rulesRegistry en cmd/launcher/main.go.

Cambios:
- agents/registry.go: nuevo registro global con sync.RWMutex
- agents/*/agent.go: cada agente llama agents.Register() en init()
- agents/_template/agent.go: placeholder AGENT_ID_PLACEHOLDER para scaffold
- cmd/launcher/main.go: elimina rulesRegistry, usa blank imports +
  agents.GetRules() para obtener reglas por agent ID

Patron: init() + blank import (estandar Go: database/sql, image codecs)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

agents/_template/agent.go

@@ -1,8 +1,16 @@
 // Package _template es un agente plantilla (no lanzable).
 // Sirve como referencia canonica para crear nuevos agentes.
+// Al crear un nuevo agente, new-agent.sh reemplaza _template y AGENT_ID_PLACEHOLDER.
 package _template
 
-import "github.com/enmanuel/agents/pkg/decision"
+import (
+	"github.com/enmanuel/agents/agents"
+	"github.com/enmanuel/agents/pkg/decision"
+)
+
+func init() {
+	agents.Register("AGENT_ID_PLACEHOLDER", Rules)
+}
 
 // Rules devuelve las reglas de este agente (vacio para el template).
 func Rules() []decision.Rule {

agents/asistente-2/agent.go

@@ -3,9 +3,14 @@
 package asistente2
 
 import (
+	"github.com/enmanuel/agents/agents"
 	"github.com/enmanuel/agents/pkg/decision"
 )
 
+func init() {
+	agents.Register("asistente-2", Rules)
+}
+
 // Rules returns the decision rules for the asistente-2 bot.
 // Note: !help is now handled by the built-in command system.
 func Rules() []decision.Rule {

agents/assistant-bot/agent.go

@@ -3,9 +3,14 @@
 package assistant
 
 import (
+	"github.com/enmanuel/agents/agents"
 	"github.com/enmanuel/agents/pkg/decision"
 )
 
+func init() {
+	agents.Register("assistant-bot", Rules)
+}
+
 // Rules returns the decision rules for the assistant bot.
 // Note: !help is now handled by the built-in command system.
 func Rules() []decision.Rule {

agents/meteorologo/agent.go

@@ -3,9 +3,14 @@
 package meteorologo
 
 import (
+	"github.com/enmanuel/agents/agents"
 	"github.com/enmanuel/agents/pkg/decision"
 )
 
+func init() {
+	agents.Register("meteorologo", Rules)
+}
+
 // Rules returns the decision rules for the meteorologo bot.
 func Rules() []decision.Rule {
 	return []decision.Rule{

agents/registry.go

@@ -0,0 +1,61 @@
+// Package agents provides a global registry for agent rule factories.
+//
+// Each agent package self-registers via init() using Register.
+// The launcher retrieves rules via GetRules without importing agent
+// packages explicitly (only blank imports are needed).
+package agents
+
+import (
+	"sync"
+
+	"github.com/enmanuel/agents/pkg/decision"
+)
+
+// RulesFunc is a factory that returns the decision rules for an agent.
+type RulesFunc func() []decision.Rule
+
+var (
+	registryMu sync.RWMutex
+	registry   = make(map[string]RulesFunc)
+)
+
+// Register adds a rule factory for the given agent ID.
+// Intended to be called from init() in each agent package.
+// Panics if the same ID is registered twice (catches copy-paste errors early).
+func Register(id string, fn RulesFunc) {
+	registryMu.Lock()
+	defer registryMu.Unlock()
+
+	if _, exists := registry[id]; exists {
+		panic("agents.Register: duplicate agent id: " + id)
+	}
+	registry[id] = fn
+}
+
+// GetRules returns the rule factory for the given agent ID.
+// Returns nil if no rules are registered (the agent is command-only).
+func GetRules(id string) RulesFunc {
+	registryMu.RLock()
+	defer registryMu.RUnlock()
+	return registry[id]
+}
+
+// RegisteredIDs returns a sorted list of all registered agent IDs.
+// Useful for debugging and diagnostics.
+func RegisteredIDs() []string {
+	registryMu.RLock()
+	defer registryMu.RUnlock()
+
+	ids := make([]string, 0, len(registry))
+	for id := range registry {
+		ids = append(ids, id)
+	}
+	return ids
+}
+
+// resetRegistry clears all registrations (for testing only).
+func resetRegistry() {
+	registryMu.Lock()
+	defer registryMu.Unlock()
+	registry = make(map[string]RulesFunc)
+}